It is desirable to produce live-time or near live-time images from imaging systems employing a collimator that is non-parallel in one or more axes and therefore produces event stream data that if left uncorrected would produce a distorted image. Less-distorted live-time or near live-time images are useful, e.g., for patient position monitoring in medical imaging. Typical methods for producing undistorted images from systems employing such collimators are processor-intensive and introduce latency not desirable for uses such as patient position monitoring.
The multifocal collimator is a two dimensional focusing collimator consisting of a variable focal length “fan” in each direction. The focal length for a location [x,y] on the collimator focal plane is described by a polynomial function of x and y. Planar images from such a collimator can be highly distorted from those of the same object viewed with parallel collimation, leading to difficulty in clinical patient setup. The distortions from use of a multifocal collimator can be both geometric distortions (imaging points in a location different from a parallel collimator) and intensity distortions (more or fewer counts imaged for a given point source depending on its location in the field of view).